The present invention is directed to electroplating processes, and in particular, processes used to manufacture the mother and stamper in the manufacture of phonograph records.
In manufacturing records, the original recording is cut with a diamond or sapphire stylus in lacquer, forming a lacquer master. The lacquer is sprayed with silver to make it electrically conductive, and then electroplated with nickel. The nickel and silver are separated from the lacquer, forming a metal master.
The metal master is then treated to remove the silver and passivate the nickel. Then another layer of nickel is plated on the face of the metal master. Because the metal master has been passivated, it is possible to mechanically separate the metal master from the second layer of nickel, which is called a "mother".
The mother is passivated, and then plated with a layer of nickel. This layer of nickel is separated from the mother and serves as a "stamper". The stamper is used for forming records on vinyl discs formed of vinyl chloride acetate copolymer.
The passivation process must not interfere with the replication of the surface being replicated. Passivation has been achieved by chemical means by either using potassium dichromate or chromic acid. However, both of these chemicals are hazardous, poisonous, and environmentally objectionable since they contain chromium.
Another passivation technique is electrolytic passivation. This is accomplished by making the part to be replicated anodic in a chemical solution by the application of direct current. Some of the chemicals used in this process, however, can be unacceptable in that they are poisonous and hazardous. Further, electrolytic passivation is a difficult process to control, being very dependent on chemical concentration and length of time of passivation.
Further, for both electrolytic passivation and chemical passivation techniques, the chemicals used are expensive and thus often reused. This can introduce contamination, corrosion, and other defects.
In view of these problems, it is apparent that there is a need for a passivation method that does not use expensive, hazardous, environmentally objectionable chemicals, and that passivates nickel surfaces without requiring precise process control.